HCG (human chorionic gonadotropin) is the pregnancy hormone. This test measures a very specific part of hCG in the blood: its beta subunit. The beta-hCG test is used to diagnose and monitor pregnancy (ectopic pregnancy—a pregnancy in which the fertilized egg is implanted and develops outside the uterus; risk of miscarriage), placental diseases (gestational trophoblastic disease such as hydatiform moles) and germ cell (ovary or testicle) tumours.
Beta-hCG is detectable within days of fertilization. Blood levels typically double every two days during the first four weeks of pregnancy and then roughly every 3.5 days at 6 weeks. HCG levels drop rapidly following childbirth or miscarriage and should be undetectable within a few weeks. If beta-hCG levels do not become undetectable, it can indicate that hCG-producing tissue is still present and that curettage may be indicated.
Positive hCG levels in men and in women outside of pregnancy is consistent with the presence of a germ cell tumour. Falling beta-hCG levels indicate that the tumour is responding to treatment, while stable or rising levels indicate that the tumour is not responding. Increases in post-treatment levels may indicate a recurrence of the disease.